Shebang to start a Python script with nohup

Question

I find it quite long to have to write:

nohup python -u myscript.py > log.txt 2>&1 &

each time I want to launch a Python script as a background process.

Is it possible to have a shebang-like first line of script like:

#!nohup python -u myscript.py > log.txt 2>&1 &
import time
while True:
    print 'hello'
    time.sleep(1)

such that a command like

run myscript.py

would automatically start the script with the command present in the first line of myscript.py?

Note: I'm looking for a single-file solution, I don't want to have to have a second file myscript.sh bash script along myscript.py to do this job.

Wouldn't it be possible to just handle the SIGHUP signal in your Python script, as well as writing to a log file instead of to stdout/stderr? — simon, Jan 09 '16 at 17:52
As an alternative to use nohup, you could just fork your program to background. See http://stackoverflow.com/questions/5975124/bring-the-current-python-program-to-background — andreas-hofmann, Jan 09 '16 at 17:56
@gurka No, I'm looking for a general solution, to be able to launch a python script with command written in the first line — Basj, Jan 09 '16 at 17:57
@andreas-hofmann : yes but then how to log stdout to file `> log.txt 2>&1 &` ? — Basj, Jan 09 '16 at 17:59

score 1 · Answer 1 · answered Jan 09 '16 at 18:14

1

I am afraid, that it is not directly possible, but you can overcome it like this:

create file run_py.sh somewhere (maybe in /home/basj/bin/ ) and make it runable:

#!/bin/bash
nohup python -u "$@" > log.txt 2>&1 &

then include in your python files this header (and make them runable)

#!/home/basj/bin/run_py.sh
print "I am in python on background with nohup now :)"

answered Jan 09 '16 at 18:14

gilhad

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`/home/basj/..` you deserve an upvote for such details – Ayush Jan 09 '16 at 18:25
Sorry but I'm really looking for a solution without a second file (see question). If I have to use 2 files, I'll just create a `myscript.sh` in the same folder, which is the simplest solution requiring 2 files. – Basj Jan 09 '16 at 23:31
and make function in .bashrc is also no way for you? https://en.wikipedia.org/wiki/Shebang_(Unix) states only one parameter is possible :( – gilhad Jan 09 '16 at 23:51

score 0 · Answer 2 · edited May 23 '17 at 12:23

0

well, this one writes to nohup.out instead of a custom file. And afaik, suspending to background using a shebang hack is not possible

#!/usr/bin/nohup python

import sys

print("to stdout")
print("to stderr",file=sys.stderr)

Giving arguments to shebang interpreter (Berkeley exec hack) does not support any form of io redirection, so your best bet might be to use a custom script as decribed in gilhad's answer

edited May 23 '17 at 12:23

Community

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1

answered Jan 09 '16 at 17:58

Ayush

3,695
1
32
42

This process won't continue in background, if I log out from SSH ? – Basj Jan 09 '16 at 18:01
it will run in background after logout, just run with a `&` as in `./script &` – Ayush Jan 09 '16 at 18:10
**disclaimer** : looks like this one appends to nohup.out only after the process dies out. – Ayush Jan 09 '16 at 18:16
argh, then it seems that this solution is not usable : the process may run for weeks, so I definetely need to read nohup.out in the meantime – Basj Jan 09 '16 at 23:27

andreas-hofmann · Answer 3 · 2016-01-10T09:51:23.323

As mentioned in the comment above, you could try to use os.fork() to send your script to background. As for stdout/stderr redirection, you can additionally overwrite the filehandles to achieve the desired result. Look at this example:

import os
import sys

class LogWriter(object):
    def __init__(self, logfile):
        self._f = open(logfile, "w")

    def write(self, data):
        self._f.write(data)
        self._f.flush()

logger = LogWriter("test.log")
sys.stdout = logger
sys.stderr = logger

if os.fork():
    sys.exit()

# Main loop
import time
while True:
    print 'hello'
    time.sleep(1)

The class LogWriter is introduced to add a flush() to every write, which occurs. The forked process remains running, if you close the ssh session which started the script.

Shebang to start a Python script with nohup

3 Answers3